Cambrian Period

Marine Deposition

544 to 505 million years ago

The Cambrian Period is the first time period of the
Paleozoic Era. During the first part of the Cambrian, the Ozarks area
remained above sea level and subject to continued erosion. Toward the
end of the Cambrian, the sea level rose or the land sank and most of the
Ozarks, including the Bryant area, became a shallow seabed. The peaks
of the St Francis Mountains of southeast Missouri remained exposed as
islands in this late Cambrian sea. The first sediment layer in this Cambrian
sea was a sandstone bed, which we now know as the LaMotte Sandstone. This
sandstone was deposited directly on the eroded Precambrian granites and
volcanic rocks. Continued subsidence or sinking of the land produced a
deeper sea further from a source of sediments. The environment was right
for the formation of carbonate sediments, and a thick sequence of limestone
(later altered to dolomite) was deposited throughout
the region. This limestone or dolomite sequence in the Bryant area is
about 1,500 feet thick and all in the subsurface. This Cambrian sea was
regional in extent, stretching from what is now Mexico into the New York
area.

Carbonate sedimentation occurs mainly in tropical waters
and paleogeographers have determined that the Ozarks area was very near
the equator during Cambrian time. A modern day equivalent would be the
area around the Bahama Islands or the Persian Gulf.

The rocks of the Cambrian worldwide contain an abundance
of fossils. Fossils were so much more common compared to the Precambrian
that it is often referred to as the Cambrian explosion. Life forms multiplied
dramatically in quantity and variety in the Cambrian seas. There are more
fossils in the Cambrian rocks for two reasons. First, there were no doubt
more marine animals living in the Cambrian seas; and second, the animals
of the Cambrian had hard shells or skeletons made of calcium carbonate
and these hard shells were far more likely to be preserved as fossils
after the animal died.